In an aircraft or like vehicle, a skin covering or outer wall surface thereof may have an opening to admit air from ambient surroundings. Admitted air may, for example, act as a coolant in an interiorly positioning heat exchanger. For reasons of aerodynamic efficiency, particularly in the case of high speed aircraft, a surface in which the opening appears is not in a confronting relation to air flows generated by movement of the vehicle through the atmosphere, but rather is generally parallel thereto. An air capturing and deflecting device is projectible from the wall surface into the passing air stream, when it is desired to admit air, and is retractable into the wall surface when an intake of air is unneeded. For convenience of description, the air capturing and deflecting device will be termed an air scoop which has open and closed positions relative to the air flows into the controlled wall surface opening.
This arrangement has certain disadvantages. In a vehicle in motion, forces applied to close the air scoop are opposed by ram air, that is, air flowing over the skin or exterior wall surface of the vehicle. In this connection, air immediately adjacent to the outer skin of an aircraft in high speed operation may have an elevated temperature making it unusable as a coolant. Under these conditions, it is desirable that the air scoop be closed. Closing is accomplished against the urging of ram air pressure. This can be quite high, requiring application of powerful closing forces. Also, a cooling system of which the air scoop is a part may have a requirement for in-flight or in-motion use and a requirement for on-the-ground or stationary use. The high pressure of ram air enables delivery of an adequate volume of air to the heat exchanger using a relatively small open flow area in the scoop. In static conditions of use, however, the open flow area required to deliver an adequate volume of air to the heat exchanger may be five to six times that needed for delivery of ram air. In the prior art, therefore, there has been little if any use of an air scoop both to admit ram air and to admit inducted air. Further, when the force applied to close the air scoop is a spring stressed in the opening of the scoop, whatever actuating mechanism is provided to open the scoop must work against resisting spring forces. These, as noted, can be quite high and must be overcome by applied opening forces.
In general, therefore, a retractable air scoop of the prior art is unsuited for plural use operation, or, at best, represents a compromise between essentially conflicting requirements. Also, the prior art scoop is relatively bulky and costly in construction since it is biased by ram air to an open position and requires relatively strong and expensive controls for its closing. In some instances, moreover, space in which to accommodate the air scoop and its extending and retracting mechanism is so limited as to present serious design problems in adapting the device to space available.